twin creek wind farm shadow flicker and blade glint … · tce has also provided the locations of...

TWIN CREEK WIND FARM

Shadow Flicker and Blade Glint Assessment Twin Creek Energy Pty Ltd

Report No.: 170894-AUME-R-01, Rev. G

Date: 26 June 2017

Status: Final

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KEY TO DOCUMENT CLASSIFICATION

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Project name: Twin Creek Wind Farm DNV GL - Energy

Renewables Advisory

Suite 25, Level 8

401 Docklands Dr

Docklands, VIC 3008

Australia

Tel: +61 3 9600 1993

Report title: Shadow Flicker and Blade Glint Assessment

Customer: Twin Creek Energy Pty Ltd

Suite 4, Level 1

760 Pacific Highway

Chatswood, NSW 2067

Australia

Contact person: Daniel Leahy

Date of issue: 26 June 2017

Project No.: 170894

Report No.: 170894-AUME-R-01, Rev. G

Document No.: 170894-AUME-R-01-G

Task and objective:

Twin Creek Wind Farm Shadow Flicker and Blade Glint Assessment

Prepared by: Verified by: Approved by:

Jules Jobin Senior Engineer,

Developer Support Services

Michael Quan Engineer,


Trenton Gilbert Principal Engineer, Head of Section,


☐ Strictly Confidential Keywords:

Twin Creek Wind Farm, shadow flicker, blade glint ☐ Private and Confidential

☐ Commercial in Confidence

☐ DNV GL only

☒ Customer’s Discretion

☐ Published

Reference to part of this report which may lead to misinterpretation is not permissible.

Rev. No. Date Reason for Issue Prepared by Verified by Approved by

A 2016-10-06 First issue – DRAFT J Jobin N Brammer T Gilbert

B 2017-03-17 Revised layout and turbine model J Jobin M Quan T Gilbert

C 2017-03-17 Minor wording changes J Jobin M Quan T Gilbert

D 2017-03-17 Minor wording changes J Jobin M Quan T Gilbert

E 2017-05-10 Changes to dwelling list J Jobin M Quan T Gilbert

F 2017-05-31 Comments regarding impact on road users J Jobin M Quan T Gilbert

G 2017-06-26 Revision to project description - Final Issue J Jobin M Quan T Gilbert

DNV GL – Report No. 170894-AUME-R-01, Rev. G – www.dnvgl.com Page i

Table of contents

EXECUTIVE SUMMARY ................................................................................................................. II

1 PROJECT DESCRIPTION ................................................................................................... 1

1.1 Project overview 1

2 PROJECT SITING/LOCALITY DESCRIPTION ......................................................................... 2

2.1 The site 2

2.2 Proposed wind farm layout 2

2.3 House locations 2

3 INTRODUCTION .............................................................................................................. 3

4 REGULATORY REQUIREMENTS .......................................................................................... 4

4.1 Shadow flicker 4

4.2 Blade glint 5

5 ASSESSMENT METHODOLOGY .......................................................................................... 6


5.2 Blade glint 9

6 ASSESSMENT RESULTS ................................................................................................. 10


6.2 Blade glint 10

7 CONCLUSIONS ............................................................................................................. 11

8 REFERENCES ................................................................................................................ 12

DNV GL – Report No. 170894-AUME-R-01, Rev. G – www.dnvgl.com Page ii

EXECUTIVE SUMMARY

Garrad Hassan Pacific Pty Ltd (“DNV GL”) has been commissioned by Twin Creek Energy Pty Ltd (“TCE”

or “the Customer”) to independently assess the expected annual shadow flicker duration in the vicinity of

the proposed Twin Creek Wind Farm. This document has been prepared pursuant to DNV GL proposal

L2C-124853-AUME-P-001-C, dated 04 March 2016, and a consultancy agreement between TCE and

DNV GL, dated 27 June 2016, and is subject to the terms and conditions therein.

Shadow flicker involves the modulation of light levels resulting from the periodic passage of a rotating

wind turbine blade between the sun and an observer. The maximum potential duration of shadow flicker

experienced at a specific location can be determined using a purely geometric analysis which takes into

account the relative position of the sun throughout the year, the wind turbines at the site, local

topography, and the viewer. This method has been used to determine the shadow flicker duration at

sensitive locations neighbouring the Twin Creek Wind Farm.

However, this analysis method tends to be conservative and typically results in over-estimation of the

number of hours of shadow flicker experienced at a dwelling /1/. Therefore, an attempt has been made

to quantify the likely reduction in shadow flicker duration due to turbine orientation and cloud cover and

hence predict the actual shadow flicker duration likely to be experienced at a dwelling.

TCE has commissioned DNV GL to assess the shadow flicker based upon the turbine layout currently

proposed for the Twin Creek Wind Farm. The proposed layout is composed of 51 Vestas V136 turbines

/2/, with a hub height of 112 m and a rotor diameter of 136 m.

TCE has also provided the locations of 289 dwellings in the area surrounding the wind farm /3/. The

digital elevation model (DEM) used to define the terrain at the site was created from a high-resolution

LiDAR DEM /4/ for the immediate site area, and SRTM1 DEM /5/ for the extended site area. These have

been used to determine the theoretical duration of shadow flicker experienced at each dwelling due to

the presence of the Twin Creek Wind Farm.

Planning SA published a draft Wind Farm Planning Bulletin (Draft SA Planning Bulletin) in 2002 /7/,

which lists shadow flicker as an issue which “need[s] to be taken into account when considering the

design of wind farms”. Similarly, the Wind Farm Development Guidelines published by the Central Local

Government Region of South Australia (Central SA Guidelines) in 2014 /8/ state that shadow flicker

“need[s] to be taken into account as part of the planning assessment” for wind farm developments.

While neither the Draft SA Planning Bulletin nor the Central SA Guidelines discuss a methodology for

assessing shadow flicker, or allowable shadow flicker durations, the Central SA Guidelines also refer to

the EPHC Draft National Wind Farm Development Guidelines (Draft National Guidelines) released in July

2010 /6/, which include recommendations for shadow flicker limits relevant to wind farms in Australia.

The Draft National Guidelines recommend that the modelled theoretical shadow flicker duration should

not exceed 30 hours per year, and that the actual or measured shadow flicker duration should not

exceed 10 hours per year. The Draft National Guidelines also recommend that the shadow flicker

duration at a dwelling be assessed by calculating the maximum shadow flicker occurring within 50 m of

the centre of a dwelling.

This assessment was based on the methodology recommended in the Draft National Wind Farm

Development Guidelines. Calculations were carried out assuming houses had either one or two stories

with window heights of either 2 m or 6 m, respectively.

DNV GL – Report No. 170894-AUME-R-01, Rev. G – www.dnvgl.com Page iii

The results indicate that, of the dwellings identified by TCE, there are locations within 50 m of a single

dwelling, identified as dwelling 147, that are predicted to experience shadow flicker, with a maximum

theoretical duration of 29.3 hours per year. Based on information provided by TCE, this dwelling is

owned by a project stakeholder, and it is not predicted to experience theoretical shadow flicker durations

in excess of the recommended limit of 30 hours per year within 50 m of the dwelling.

When considering the predicted actual shadow flicker duration, which takes into account the reduction in

shadow flicker due to turbine orientation and cloud cover, the maximum shadow flicker duration in the

vicinity of dwelling 147 is predicted to reduce to 11.7 hours per year, which is above the recommended

limit for actual shadow flicker of 10 hours per year within 50 m of the house location. It should however

be noted that the Draft National Guidelines considers compliance in cases where the maximum

theoretical duration limit is satisfied.

The prediction of the actual shadow flicker duration does not take into account any reduction due to low

wind speed, vegetation, or other shielding effects around each house in calculating the number of

shadow flicker hours. Therefore, the values presented may still be regarded as conservative. The effects

of shadow flicker can also be reduced through a number of mitigation measures such as the installation

of screening structures or planting of trees (if not already in place) to block shadows cast by the turbines,

or the use of turbine control strategies which shut down turbines when shadow flicker is likely to occur.

It should also be noted that, with regards to shadow flicker impact on passing vehicles, the Draft

National Guidelines state that “there is a negligible risk associated with distraction of vehicle drivers who

experience shadow flicker”. Therefore, shadow flicker impact on passing vehicles is not expected to be a

problem for the proposed wind farm.

Blade glint involves the reflection of light from a turbine blade, and can be seen by an observer as a

periodic flash of light coming from the wind turbine. Blade glint is not generally a problem for modern

turbines provided non-reflective coatings are used for the surface of the blades.

DNV GL – Report No. 170894-AUME-R-01, Rev. G – www.dnvgl.com Page 1

1 PROJECT DESCRIPTION

Twin Creek Energy Pty Ltd (“TCE”) proposes to develop the Twin Creek Wind Farm within the mid north

area of South Australia. The site of the proposed wind farm is approximately 90 km northeast of

Adelaide and northeast of Kapunda.

1.1 Project overview

TCE has advised that the proposed wind farm will consist of the following components:

Up to 51 Wind Turbines Generators (WTG)

o Each WTG has a capacity up to 3.6 Megawatts (MW), with a total installed wind capacity up

to 183 MW

o Overall height of turbines would be up to 180 metres at the blade tip

Associated hard standing areas and access roads

Operations and maintenance building and compound with associated car parking

Two electrical substations

50 MW battery energy storage facility

Overhead and underground electrical cable reticulation

Overhead transmission line for approximately 15 kilometres from the on-site substation to the

existing overhead Robertstown - Tungkillo transmission line east of Truro

Meteorological masts for measuring wind speed and other climatic conditions

Temporary construction facilities including a borrow pit and concrete batching plant facilities.


2 PROJECT SITING/LOCALITY DESCRIPTION

2.1 The site

The proposed Twin Creek Wind Farm site is located in South Australia, approximately 80 km northeast of

Adelaide, near the town of Kapunda. The general location of the site is shown in Figure 1.

The site area is located on a series of hills and ridges, and is mostly composed of complex terrain, with

turbine base elevations ranging from approximately 215 m to 461 m. Ground cover at the majority of

the site consists of cleared fields and grassland.

The digital elevation model (DEM) used to define the terrain at the site was created from a high

resolution LiDAR DEM /4/ for the immediate site area, and SRTM1 DEM /5/, for the extended site area.

2.2 Proposed wind farm layout

The shadow flicker modelling conducted for this assessment assumed the proposed wind farm will be

composed of 51 wind Vestas V136 turbines, with the turbine dimensions relevant to the shadow flicker

assessment as follows:

rotor diameter of 136 m

hub height of 112 m.

A list of coordinates of the proposed 51 turbine locations is provided in Table 1.

2.3 House locations

A list of houses neighbouring the wind farm was supplied to DNV GL by TCE /3/. The coordinates of the

dwellings found within 1410 m of the turbine locations are presented in Table 2.

DNV GL has assumed that all listed houses are potential inhabited residential locations. Dwellings

situated more than 1410 m from turbine locations will have predicted annual shadow flicker durations of

zero hours due to the shadow flicker distance limit assumed for the analysis, as discussed further in

Section 4.1 and Section 5.1.2.

It should be noted that DNV GL has not carried out a detailed and comprehensive survey of house

locations in the area and is relying on information provided by the Customer.


3 INTRODUCTION

Garrad Hassan Pacific Pty Ltd (“DNV GL”) has been commissioned by TCE (“the Customer”) to

independently assess the expected annual shadow flicker duration in the vicinity of the proposed Twin

Creek Wind Farm. The results of this work are reported here. This document has been prepared pursuant

to DNV GL proposal L2C-124853-AUME-P-001-C, dated 04 March 2016, and a consultancy agreement

between TCE and DNV GL, dated 27 June 2016, and is subject to the terms and conditions therein.


4 REGULATORY REQUIREMENTS

4.1 Shadow flicker

Planning SA published a draft Wind Farm Planning Bulletin (Draft SA Planning Bulletin) in 2002 /7/,

which lists shadow flicker as an issue which “need[s] to be taken into account when considering the

design of wind farms”. Similarly, the Wind Farm Development Guidelines published by the Central Local

Government Region of South Australia (Central SA Guidelines) in 2014 /8/ state that shadow flicker

“need[s] to be taken into account as part of the planning assessment” for wind farm developments.

While neither the Draft SA Planning Bulletin nor the Central SA Guidelines discuss a methodology for

assessing shadow flicker, or allowable shadow flicker durations, the Central SA Guidelines also refer to

the EPHC Draft National Wind Farm Development Guidelines (Draft National Guidelines) released in July

2010 /6/, which include recommendations for shadow flicker limits relevant to wind farms in Australia

The Draft National Guidelines recommend that the modelled theoretical shadow flicker duration should

not exceed 30 hours per year, and that the actual or measured shadow flicker duration should not

exceed 10 hours per year. The Draft National Guidelines also recommend that the shadow flicker

duration at a dwelling be assessed by calculating the maximum shadow flicker occurring within 50 m of

the centre of a dwelling.

These limits are assumed to apply to a single dwelling, and it is noted that there is no requirement under

either the Central SA Guidelines, Draft SA Planning Bulletin or Draft National Guidelines to assess

shadow flicker durations at locations other than in the vicinity of dwellings.

The Draft National Guidelines also provide background information, a proposed methodology, and a suite

of assumptions for assessing shadow flicker durations in the vicinity of a wind farm.

The impact of shadow flicker is typically only significant up to a distance of around 10 rotor diameters

from a turbine /9/ or approximately 800 m to 1400 m for modern wind turbines (which typically have

rotor diameters of 80 m to 140 m). Beyond this distance limit the shadow is diffused such that the

variation in light levels is not likely to be sufficient to cause annoyance. This issue is discussed in the

Draft National Guidelines where it is stated that:

“Shadow flicker can theoretically extend many kilometres from a wind turbine. However the

intensity of the shadows decreases with distance. While acknowledging that different individuals

have different levels of sensitivity and may be annoyed by different levels of shadow intensity, these

guidelines limit assessment to moderate levels of intensity (i.e., well above the minimum

theoretically detectable threshold) commensurate with the nature of the impact and the

environment in which it is experienced.”

The Draft National Guidelines therefore suggest a distance equivalent to 265 times the maximum blade

chord as an appropriate limit, which corresponds to approximately 800 m to 1325 m for modern wind

turbines (which typically have maximum blade chord lengths of 3 m to 5 m).

The Draft National Guidelines also provide commentary on the negligible risk of distraction of vehicle

drivers, and state the following:

“There is a negligible risk associated with distraction of vehicle drivers who experience shadow

flicker, for the following reasons:

Shadow flicker is little different for a vehicle in motion than the effect of shadows from trees

on the side of the road or high passing vehicles, neither of which represent a significant risk

in terms of road transport.


In spite of extensive searches, no references to motor vehicle accidents caused by this

phenomenon have been found.

It is noted, however, that until wind farms become widespread in Australia they will represent a

novelty that could cause distraction for drivers (regardless of shadow flicker). Consideration should

be given to development of viewing areas for wind farms close to high volume roads.

4.2 Blade glint

The Draft National Guidelines provide guidance on blade glint and state that:

“The sun’s light may be reflected from the surface of wind turbine blades. Blade Glint has the

potential to annoy people. All major wind turbine manufacturers currently finish their blades with a

low reflectivity treatment. This prevents a potentially annoying reflective glint from the surface of

the blades and the possibility of a strobing reflection when the turbine blades are spinning.

Therefore the risk of blade glint from a new development is considered to be very low.”


5 ASSESSMENT METHODOLOGY

5.1 Shadow flicker

5.1.1 Overview

Shadow flicker may occur under certain combinations of geographical position and time of day, when the

sun passes behind the rotating blades of a wind turbine and casts a moving shadow over neighbouring

areas. When viewed from a stationary position the moving shadows cause periodic flickering of the light

from the sun, giving rise to the phenomenon of ‘shadow flicker’.

The effect is most noticeable inside buildings, where the flicker appears through a window opening. The

likelihood and duration of the effect depends upon a number of factors, including:

direction of the property relative to the turbine

distance from the turbine (the further the observer is from the turbine, the less pronounced the

effect will be)

wind direction (the shape of the shadow will be determined by the position of the sun relative to

the blades which will be oriented to face the wind)

turbine height and rotor diameter

time of year and day (the position of the sun in the sky)

weather conditions (cloud cover reduces the occurrence of shadow flicker).

5.1.2 Theoretical modelled duration

The theoretical number of hours of shadow flicker experienced annually at a given location can be

calculated using a geometrical model which incorporates the sun path, topographic variation over the

site area, and wind turbine details such as rotor diameter and hub height.

The wind turbines have been modelled assuming they are spherical objects, which is equivalent to

assuming the turbines are always oriented perpendicular to the sun-turbine vector. This assumption will

mean the model calculates the maximum duration for which there is potential for shadow flicker to occur.

In line with the methodology proposed in the Draft National Guidelines, DNV GL has assessed the

shadow flicker at the surveyed house locations and has determined the highest shadow flicker duration

within 50 m of each of the provided house locations.

Shadow flicker has been calculated at dwellings at heights of 2 m, to represent ground floor windows,

and 6 m, to represent second floor windows. The shadow receptors are simulated as fixed points,

representing the worst case scenario, as real windows would be facing a particular direction. The shadow

flicker calculations for dwelling locations have been carried out with a temporal resolution of 1 minute

(meaning that if shadow flicker is predicted to occur in any 1-minute period, the model records this as

1 minute of shadow flicker) and a line-of-sight resolution of 1 m. The shadow flicker map was generated

using a temporal resolution of 5 minutes and a line-of-sight resolution of 5 m to reduce computational

requirements to acceptable levels.

As part of the shadow flicker assessment, it is necessary to make an assumption regarding the

maximum length of a shadow cast by a wind turbine that is likely to cause annoyance due to shadow

flicker. The UK wind industry considers that a limit of 10 rotor diameters is appropriate /9/, while the

Draft National Guidelines suggest a distance equivalent to 265 times the maximum blade chord as an


appropriate limit. For the current assessment, DNV GL has implemented a maximum shadow length of

10 times the rotor diameter, or 1360 m, based on the turbine dimensions specified in Section 2.2.

The model also makes the following assumptions and simplifications:

there are clear skies every day of the year

the blades of the turbines are always perpendicular to the direction of the line of sight from the

location of interest to the sun

the turbines are always rotating.

The first two of these items are addressed in the calculation of the predicted actual shadow flicker

duration as described in Section 5.1.4. The third item means that the results generated by the model

may be slightly conservative, as there will be some periods of time when the turbines are not rotating,

but this is considered unlikely to have a significant impact on the results.

The settings used to execute the model can be seen in Table 3.

To illustrate typical results, an indicative shadow flicker map for a turbine located in a relatively flat area

is shown in Figure 2. The geometry of the shadow flicker map can be characterised as a butterfly shape,

with the four protruding lobes corresponding to slowing of solar north-south travel around the summer

and winter solstices for morning and evening. The lobes to the north of the indicative turbine location

result from the summer solstice and conversely the lobes to the south result from the winter solstice.

The lobes to the west result from morning sun while the lobes to the east result from evening sun. When

the sun is low in the sky, the length of shadows cast by the turbine increases, increasing the area around

the turbine affected by shadow flicker.

5.1.3 Factors affecting duration

Shadow flicker duration calculated in this manner overestimates the annual number of hours of shadow

flicker experienced at a specified location for several reasons, including:

1. The wind turbine will not always be oriented such that its rotor is in the worst case position (i.e.

perpendicular to the sun-turbine vector). Any other rotor orientation will reduce the area of the

projected shadow and hence the shadow flicker duration.

The wind speed frequency distribution or wind rose at the site can be used to determine probable

turbine orientation and to calculate the resulting reduction in shadow flicker duration.

2. The occurrence of cloud cover has the potential to significantly reduce the number of hours of

shadow flicker.

Cloud cover measurements recorded at nearby meteorological stations may be used to estimate

probable levels of cloud cover and to provide an indication of the resulting reduction in shadow

flicker duration.

3. Aerosols (moisture, dust, smoke, etc.) in the atmosphere have the ability to influence shadows

cast by a wind turbine.

The length of the shadow cast by a wind turbine is dependent on the degree that direct sunlight

is diffused, which is in turn dependent on the amount of dispersants (humidity, smoke, and other

aerosols) in the path between the light source (sun) and the receiver.

4. The modelling of the wind turbine rotor as a sphere rather than individual blades results in an

overestimate of shadow flicker duration.


Turbine blades are of non-uniform thickness with the thickest part of the blade (maximum chord)

close to the hub and the thinnest part (minimum chord) at the tip. Diffusion of sunlight, as

discussed above, results in a limit to the maximum distance that a shadow can be perceived.

This maximum distance will also be dependent on the thickness of the turbine blade, and the

human threshold for perception of light intensity variation. As such, a shadow cast by the blade

tip will be shorter than the shadow cast by the thickest part of the blade.

5. The analysis does not consider that when the sun is positioned directly behind the wind turbine

hub, there is no variation in light intensity at the receiver location and therefore no shadow

flicker.

6. The presence of vegetation or other physical barriers around a shadow receptor location may

shield the view of the wind turbine, and therefore reduce the incidence of shadow flicker.

7. Periods where the wind turbine is not in operation due to low winds, high winds, or for

operational and maintenance reasons will also reduce the annual shadow flicker duration.

5.1.4 Predicted actual duration

As discussed above in Section 5.1.3, there are a number of factors which may reduce the incidence of

shadow flicker, such as cloud cover and variation in turbine orientation, that are not taken into account

in the calculation of the theoretical shadow flicker duration. Exclusion of these factors means that the

theoretical calculation is likely to be conservative. An attempt has been made to quantify the likely

reduction in shadow flicker duration due to these effects and therefore predict the actual shadow flicker

duration likely to be experienced at a dwelling.

Cloud cover is typically measured in ‘oktas’ or eighths of the sky covered with cloud. DNV GL has

obtained climate statistics data from a number of nearby Bureau of Meteorology (BoM) stations. From

the stations assessed, the following five stations had the required cloud cover data available:

023307 Kapunda /10/

023373 Nuriootpa PIRSA /11/

023343 Rosedale (Turretfield Research Centre) /12/

023763 Mount Crawford Forest Headquarters /13/

023083 Edinburgh RAAF /14/

The cloud cover data used for the assessment consists of twice daily approximations of the percentage of

cloud cover visible across the sky provided as monthly averages.

The average annual cloud cover value obtained from readings at 9 am and 3 pm at these stations is 4.1

oktas. As such, on an average day, approximately 52% of the sky in the vicinity of the wind farm is

covered with clouds. An assessment of the likely reduction in shadow flicker duration due to cloud cover

was conducted on a monthly basis, with average monthly cover ranging from approximately 39% to

63%.

Although it is not possible to definitively calculate the effect of cloud cover on shadow flicker duration, a

reduction in the shadow flicker duration proportional to the amount of cloud cover is a reasonable

assumption.

Similarly, turbine orientation can have an impact on the shadow flicker duration. The shadow flicker

impact is greatest when the turbine rotor plane is approximately perpendicular to a line joining the sun

and an observer, and a minimum when the rotor plane is approximately parallel to a line joining the sun


and an observer. A wind direction frequency distribution was derived from data collected by the site

mast, and was used to estimate the reduction in shadow flicker duration due to rotor orientation. The

measured wind rose is shown overlaid on the indicative shadow flicker map in Figure 2. An assessment

of the likely reduction in shadow flicker duration due to variation in turbine orientation was conducted on

an annual basis.

It should be noted that the method prescribed by the Draft National Guidelines for assessing actual

shadow flicker duration recommends that only reductions due to cloud cover, and not turbine orientation,

be included. However, DNV GL considers that the additional reduction due to turbine orientation is

appropriate as the projected area of the turbine, and therefore the expected shadow flicker duration, is

reduced when the turbine rotor is not perpendicular to the line joining the sun and dwelling. Due to

limitations in the availability of suitable cloud cover data, the methodology used in this assessment also

deviates somewhat from the method recommended by the Draft National Guidelines for assessing the

reduction in shadow flicker due to cloud cover. However, considering the available cloud cover data, the

approach described above is deemed to provide a reasonable estimate of the likely impact of cloud cover

on the shadow flicker duration.

No attempt has been made to account for vegetation or other shielding effects around each shadow

receptor in calculating the shadow flicker duration. Similarly, turbine shutdown has not been considered.

It is therefore likely that the adjusted shadow flicker durations presented here can still be regarded as a

conservative assessment.

5.2 Blade glint

Blade glint involves the regular reflection of the sun off rotating turbine blades. Its occurrence depends

on a combination of circumstances arising from the orientation of the nacelle, angle of the blade, and the

angle of the sun. The reflectiveness of the surface of the blades is also important. Blade glint is not

generally a problem for modern wind turbines, provided the blades are coated with a non-reflective paint.


6 ASSESSMENT RESULTS

6.1 Shadow flicker

A shadow flicker assessment was carried out at all provided dwelling locations, or ‘receptors’, located

within 1410 m of the proposed Twin Creek Wind Farm, as outlined in Table 2.

The theoretical predicted shadow flicker durations at all dwellings identified to be affected by shadow

flicker are presented in Table 4. The maximum predicted theoretical shadow flicker durations within

50 m of these receptors are also presented in this table. In addition to the tabular results, the theoretical

annual occurrence of shadow flicker is shown graphically in Figure 3, for the worst-case location within

50 m of dwelling 147.

The theoretical predicted shadow flicker durations are also shown in the form of a shadow flicker map in

Figure 4 and as shadow flicker contours in Figure 6. The shadow flicker values presented in these maps

represent the maximum theoretical shadow flicker duration, considering the results at 2 m and 6 m

above ground for each modelled grid point.

The results indicate that, out of the dwellings identified by TCE, a single dwelling is predicted to

experience some shadow flicker based on the methodology recommended by the Draft National

Guidelines. Furthermore, none of the locations modelled within 50 m of the dwelling are predicted to

experience shadow flicker exceeding the limit of 30 hours per year, as recommended by the Draft

National Guidelines.

An assessment of the level of conservatism associated with the theoretical results has been conducted

by calculating the possible reduction in shadow flicker duration due to turbine orientation (based on the

wind measurements obtained at the site) and cloud cover. These adjusted results are presented as

predicted actual shadow flicker durations in Table 4 and Figure 5. Consideration of turbine orientation

and cloud cover reduces the predicted shadow flicker duration at dwelling 147 by approximately 52%,

resulting in an actual shadow flicker duration within 50 m of the dwelling location that is above the limit

of 10 hours per year, as recommended by the Draft National Guidelines. It should however be noted that

the Draft National Guidelines considers compliance in cases where the maximum theoretical duration

limit is satisfied.

If shadow flicker presents a problem, its effects can be reduced through a number of measures. These

include the installation of screening structures or planting of trees to block shadows cast by the turbines,

the use of turbine control strategies which shut down turbines when shadow flicker is likely to occur, or

micro-siting of turbines.

6.2 Blade glint

As discussed in Section 5.2, blade glint is not generally a problem for modern wind turbines provided

that the blades are coated with a non-reflective paint.


7 CONCLUSIONS

An analysis has been conducted to determine the annual duration of shadow flicker experienced at

dwellings in the vicinity of the proposed Twin Creek Wind Farm, based on the methodology proposed in

the Draft National Guidelines. The results of the assessment are presented in the form of shadow flicker

maps in Figure 4 to Figure 6. The shadow flicker results for each house location predicted to be affected

by shadow flicker are also listed in Table 4.

The theoretical shadow flicker modelling conducted at the site indicates that no dwelling is expected to

exceed the 30-hr limit recommended by the Draft National Guidelines. Upon consideration of the likely

shadow flicker reduction due to could cover and rotor orientation, the maximum shadow flicker duration

expected within 50 m of dwelling 147 is expected to exceed the 10-hr limit recommended by the Draft

National Guidelines; with a value of 11.7 hr/yr. It should however be noted that the Draft National

Guidelines considers compliance in cases where the maximum theoretical duration limit is satisfied.

It should be noted that the calculation of predicted actual shadow flicker duration does not take into

account any reduction in shadow flicker hours due to low wind speed, vegetation, or other shielding

effects. Therefore, the values presented may still be regarded as a conservative assessment.

If shadow flicker presents a problem, mitigation strategies to reduce the duration of shadow flicker

experienced at a dwelling can include: installation of screening structures or planting of trees to block

shadows cast by the turbines, use of turbine control strategies which shut down turbines when shadow

flicker is likely to occur, or relocation of turbines.

It should also be noted that, with regards to shadow flicker impact on passing vehicles, the Draft

National Guidelines state that “there is a negligible risk associated with distraction of vehicle drivers who

experience shadow flicker”. Therefore, shadow flicker impact on passing vehicles is not expected to be a

problem for the proposed wind farm.

Blade glint is not likely to be an issue provided non-reflective coatings are used on the turbine blades.


8 REFERENCES

/1/ “Influences of the opaqueness of the atmosphere, the extension of the sun and the rotor blade

profile on the shadow impact of wind turbines”, Freund H-D, Kiel F.H., DEWI Magazine No. 20, Feb

2002, pp43-51.

/2/ “Turbine Layout PAUStwc025.xlsx”, MS Excel format, downloaded from project data room,

01 March 2016.

/3/ “HouselayoutDAUStwc005_SentToDNVGL_20170508.xlsx”, MS Excel format, attachment to email

from D. Leahy (TCE) to J. Jobin (DNV GL), 09 May 2017.

/4/ “TwinCreekLiDAR2016_xyz_1mDEM”, LiDAR DEM data tiles in XYZ format, downloaded from

project data room, 04 July 2016.

/5/ Shuttle Radar Topography Mission (SRTM) - 1 arc-second resolution, National Aeronautics and

Space Administration (NASA), data tiles downloaded from USGS EarthExplorer, 05 July 2016.

/6/ “National Wind Farm Development Guidelines – Public Consultation Draft”, Environment Protection

and Heritage Council (EPHC), July 2010.

/7/ “Planning Bulletin – Wind Farms – Draft for Consultation”, Planning SA, August 2002.

/8/ “Wind Farm Development Guidelines for Developers and Local Government Planners”, Central

Local Government Region of South Australia, June 2014.

/9/ “Planning for Renewable Energy – A Companion Guide to PPS22”, Office of the Deputy Prime

Minister, UK, 2004.

/10/ “Climate statistics for Australian locations – Kapunda)”, Bureau of Meteorology, viewed 19

September 2016, http://www.bom.gov.au/climate/averages/tables/cw_023307_All.shtml.

/11/ “Climate statistics for Australian locations – Nuriootpa pirsa”, Bureau of Meteorology, viewed 19


/12/ “Climate statistics for Australian locations – Rosedale (Turretfield Research Centre)”, Bureau of

Meteorology, viewed 19 September 2016,

http://www.bom.gov.au/climate/averages/tables/cw_023343_All.shtml.

/13/ “Climate statistics for Australian locations – Mount Crawford Forest Headquarters”, Bureau of

Meteorology, viewed 19 September 2016,

http://www.bom.gov.au/climate/averages/tables/cw_023763_All.shtml.

/14/ “Climate statistics for Australian locations – Edinburgh RAAF”, Bureau of Meteorology, viewed 19


http://earthexplorer.usgs.gov/

http://www.bom.gov.au/climate/averages/tables/cw_023307_All.shtml






List of Tables

Table 1 Turbine layout for the proposed Twin Creek Wind Farm ...................................................... 14

Table 2 Dwelling locations within 1410 m of turbines at the Twin Creek Wind Farm ........................... 14

Table 3 Shadow flicker model settings for theoretical shadow flicker calculation ................................ 15

Table 4 Theoretical and predicted actual annual shadow flicker durations for the proposed Twin Creek Wind Farm ................................................................................................................................ 16

List of Figures

Figure 1 Location of the Twin Creek Wind Farm ............................................................................ 17

Figure 2 Indicative shadow flicker map and wind direction frequency distribution .............................. 18

Figure 3 Worst case annual theoretical shadow flicker occurrence at dwelling 147 ............................. 19

Figure 4 Theoretical annual shadow flicker duration map for the proposed Twin Creek Wind Farm, considering shadow flicker at 2 m and 6 m above ground level ........................................................ 20

Figure 5 Predicted actual annual shadow flicker duration map for the proposed Twin Creek Wind Farm, considering shadow flicker at 2 m and 6 m above ground level ........................................................ 21

Figure 6 Theoretical annual shadow flicker duration contours for the proposed Twin Creek Wind Farm, considering shadow flicker at 2 m and 6 m above ground level ........................................................ 22


Table 1 Turbine layout for the proposed Twin Creek Wind Farm

WTG ID

Easting1 [m]

Northing1 [m]

Base elevation

[m]

WTG ID

Easting1 [m]

Northing1 [m]

Base elevation

[m]

T1 321026 6200205 388 T27 323772 6203076 437

T2 321360 6200955 376 T28 322719 6203537 442

T3 322403 6200826 438 T29 322046 6203820 423

T4 321993 6201019 435 T30 321713 6204052 406

T5 321620 6201367 412 T31 321308 6204303 421

T6 320952 6201223 374 T32 321201 6204679 384

T7 319882 6201452 349 T33 324338 6203141 454

T8 320250 6201090 329 T34 323586 6203550 425

T9 322950 6201222 432 T35 322782 6204095 455

T10 322538 6201521 436 T36 322249 6204368 453

T11 322022 6201882 412 T37 321973 6204642 418

T12 322572 6201943 406 T38 324342 6203539 480

T13 322322 6202456 380 T40 324060 6203843 446

T14 320971 6202391 349 T42 323325 6204676 427

T15 320036 6202498 341 T43 322719 6204664 453

T16 320224 6203111 350 T44 323646 6204246 425

T17 321816 6202690 392 T45 323837 6204811 439

T18 323643 6202084 428 T46 323611 6205227 447

T19 323292 6202686 425 T47 323205 6205593 470

T20 322886 6202903 407 T48 323115 6205082 462

T21 322371 6203086 426 T49 322641 6205411 423

T22 321826 6203111 392 T50 321133 6203686 364

T23 321590 6203414 404 T51 321050 6202928 347

T24 320666 6204049 353 T52 321374 6201812 356

T25 324225 6202148 432 T53 323112 6202183 415

T26 323887 6202670 451

Notes:

1. Coordinate system: MGA Zone 54, GDA94 datum.

Table 2 Dwelling locations within 1410 m of turbines at the Twin Creek Wind Farm

House ID

Easting1 [m]

Northing1 [m]

Nearest turbine ID

Distance to nearest turbine

[m]

74 320270 6205615 T32 1320

75 321830 6206405 T49 1283

147 319969 6205165 T24 1316

Notes:



Table 3 Shadow flicker model settings for theoretical shadow flicker calculation

Model setting Value

Maximum shadow length 1360 m

Year of calculation 2029

Minimum elevation of the sun 3°

Time step 1 min (5 min for map)

Rotor modelled as Sphere (disc for turbine orientation reduction calculation)

Sun modelled as Disc

Offset between rotor and tower None

Receptor height (single storey) 2 m

Receptor height (double storey) 6 m

Locations used for determining maximum shadow

flicker within 50 m of each dwelling

25 m grid centred on house location and 8 points evenly

spaced on a 50 m radius circle centred on the house location

Grid resolution for shadow flicker mapping 10 m


Table 4 Theoretical and predicted actual annual shadow flicker durations for the proposed Twin Creek Wind Farm

House

ID1

Easting2

[m]

Northing2

[m]

Contributing

turbines

Theoretical annual Predicted actual annual3

At dwelling

[hr/yr]

Max within 50 m of dwelling

[hr/yr]

At dwelling

[hr/yr]

Max within 50 m of dwelling

[hr/yr]

SF at 2 m SF at 6 m SF at 2 m SF at 6 m SF at 2 m SF at 6 m SF at 2m SF at 6 m

147 319969 6205165 T32 23.8 24.2 29.1 29.3 9.4 9.7 11.7 11.6

Annual duration limits 30 30 10 10

Notes:

1. Dwellings identified in Table 2 with no shadow flicker limit have been omitted from this table.


3. Considering likely reductions in shadow flicker duration due to cloud cover and turbine orientation.


Figure 1 Location of the Twin Creek Wind Farm


Figure 2 Indicative shadow flicker map and wind direction frequency distribution


Figure 3 Worst case annual theoretical shadow flicker occurrence at dwelling 147


Figure 4 Theoretical annual shadow flicker duration map for the proposed Twin Creek Wind Farm, considering shadow flicker at 2 m and 6 m above ground level


Figure 5 Predicted actual annual shadow flicker duration map for the proposed Twin Creek Wind Farm, considering shadow flicker at 2 m and 6 m above ground level


Figure 6 Theoretical annual shadow flicker duration contours for the proposed Twin Creek Wind Farm, considering shadow flicker at 2 m and 6 m above ground level

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